Method for boring and placing bolts for imbedding adhesively and device for carrying out this method

ABSTRACT

A method and device for drilling and setting adhesive anchor bolts close to the mine face during the cutting operation of a tunneling or mining machine which is capable of being displaced on a traveling mechanism and includes a cutting cylinder or cutting head rotationally mounted on a cantilever arm pivotable in a vertical direction, and optionally in a horizontal direction. The method is carried out in a manner where the substantially horizontal forward movement of the cantilever arm at break-in cutting is detected and a signal is generated during break-in cutting to block commencement of a working cycle for drilling and anchoring. A controller ( 16 ) for excavation of material on the mine face is networked with a controller ( 15 ) for actuation of the anchor drilling and setting device ( 10 ) via radio, electrical or optical lines ( 17 ).

The invention relates to a method for drilling and setting adhesiveanchor bolts close to the mine face during the cutting operation of atunneling or mining machine which is capable of being displaced on atraveling mechanism and includes a cutting cylinder or cutting headrotationally mounted on a pivotable cantilever arm and pivotable in thevertical direction, and optionally also in the horizontal direction, aswell as a device for carrying out this method.

Tunneling machines with integrated anchor drilling and setting devicesare, for instance, described in WO 99/14463. In that known machine atleast one support capable of being braced between the roof and the flooris provided near the mine face. In order to improve the support relativeto the machine frame, an articulated strut is additionally provided, bywhich the support is hinged to the rear portion of the machine. Inprinciple, such a device enables anchoring near the mine face. Yet, thequality of the anchor bore is, of course, limited on account ofvibrations of the machine frame, an effective support being feasibleonly relative to the machine frame and the machine frame itself beingsubject to vibrations during tunneling or material working as a functionof the respectively chosen cutting parameters. Supports of that type areonly insufficiently able to take up horizontal forces. During break-incutting, the cantilever arm is moved in the direction towards the mineface along with the cutting tools, and in that phase of the cuttingprocedure the reaction forces have to be taken up as frictional forceson the respective bracings and, in particular, on the crawler mechanismand on the roof bar, respectively. If, as usually happens with a miningprocess, the break-in cutting procedure is started close to the roof andthe mining or excavation cycle takes place subsequently by a verticaldownward movement of the cantilever arm, the respective reaction forceswill then be substantially better absorbed by application forces of thetraveling mechanism on the floor, so that even the bracing provided nearthe mine face can be kept free of vibrations more easily. However, thetroublefree operation of the anchor drilling and setting devices is notreadily ensured at any time during the cutting procedure, particularlywhen winning hard coal or cutting hard rock. It was, therefore, proposedto design the anchor boring and setting device so as to be completelyindependent of the tunneling or mining machine and displace itseparately, such a device being, for instance, described in U.S. Pat.No. 4,229,124. A device of this type is suitable for the introduction ofadhesive anchor bolts, such a completely separate realization of theanchor drilling and setting device from the advance working machinerendering feasible a high degree of automation.

Anchor drilling and setting devices capable of being largely automatedare basically known. EP-A1-0 124 658, for instance, describes an anchordrilling and setting device of this type, by which a remote control ofthe individual steps required, namely drilling, inserting the adhesivecartridges and mounting the anchor, is feasible in order to therebyenable the operating personnel to keep off the unprotected roof region.Yet, a cantilever arm arranged on a separately movable drill carriage isalso provided in that device. U.S. Pat. No. 4,165,789 describes ananchor drilling and setting device controlled by a microcomputer, inwhich any risk of damage to the drill head or bending of the drill rodassembly is to be avoided by the appropriate incremental alteration ofthe parameters for the drilling process. With such a relatively complexcontrol, the advance movement and number of revolutions of the drillingdevice are each monitored and, while keeping constant one of those twoparameters, e.g. the advance movement, the other parameter, e.g. thenumber or revolutions, is changed in increments in order to therebyachieve the maximum drilling performance. A device of this type cannotbe directly arranged on an advance working machine either, since theparameters selected to optimize the drilling performance for the settingof the anchors will in no way take into account the respective operatingparameters of the cutting machine.

Finally, an anchor drilling and setting device which is directlyconnected with the frame of a tunneling or driving machine is describedin GB 2 210 081 A. The decoupling of movements of the machine frame inthat case is proposed to be accomplished by the telescopic design of thesupport of the anchor drilling and setting device relative to themachine frame, whereby a device of this type can naturally be used onlyon the rear end of a machine such that the distance between the mineface and the site on which an effective anchorage can be realized willbecome relative large.

The invention aims to provide a method and device of the initiallydefined kind, by which drilling and setting anchor bolts close to themine face can be effected in an automated manner without entailingimpairments by the largely simultaneous advance working of the track orwinning of material. The method according to the invention, inparticular, is to offer the opportunity to increase the safety near themine face by substantially simpler and quicker control means for theanchor drilling and setting devices.

To solve this object, the method according to the invention isessentially characterized in that the substantially horizontal movementof the cantilever arm at break-in cutting is detected and a signal isgenerated during break-in cutting to block the start of a working cyclefor drilling and anchoring. By detecting the parameters that arecritical for a safe anchorage and support of the anchor drilling andsetting device during the cutting procedure or advance working process,and blocking the operation of anchor drilling and setting devices onlyif a safe support is not guaranteed, the time available for the preciseintroduction of anchors near the mine face is substantially extended.According to the invention, only that period of time over which thecutting cylinder or cutting tools are advanced into the mine face isthus factored out, since a precise anchor bore appears uncertain andlikely to be impeded merely during the horizontal movement of thecantilever arm or machine into the mine face on account of the highreaction forces occurring in the event of hard rock or hard coal. Duringthe excavation process, in which the cantilever arm is moved in thevertical direction from the roof to the floor, the reaction forces arereliably taken up via the traveling mechanism of the advance workingmachine or winning machine, and a machine support arranged close to themine face can thus be effectively kept free of vibrations and movementsso as to enable the making of precise bores without involving anyexpensive monitoring of the drilling parameters of the anchor drillingand setting devices. Advantageously, the method according to theinvention is realized in a manner that the start of an anchor drillingand setting procedure is enabled upon completion of the horizontalmovement of the machine or cantilever arm into the mine face. Overall,only a short span is thus unavailable for the actuation of the anchordrilling and setting device during advance working or material winning,and it is feasible in the main to realize an effective securement of theroof in the immediate vicinity of the mine face at a high speed.

As initially mentioned, the device according to the invention forcarrying out the above method requires a tunneling or mining machine inwhich a pivotable cantilever arm to which a cutting cylinder isrotationally mounted is provided, thus implying a defined operationmethod of such a tunneling or mining machine. Such devices, in fact,serve to make a break-in cut near the roof first and continue winning oradvance working after this by vertically pivoting or, when using acutting head, horizontally and vertically pivoting the cantilever arm.The device according to the invention is essentially characterized inthat the control means for the excavation of material on the mine faceis networked with the control means for the actuation of the anchordrilling and setting device via radio, electrical or optical lines. Thetype of control means respectively chosen for the excavation of materialand for the actuation of the anchor drilling and setting devices in thiscase is freely selectable within a broad range, wherein known controlmeans for the excavation of material and known control means for theactuation of anchor drilling and setting devices are applicable, itbeing merely required to appropriately network these means in order toensure the mutual blockage at critical moments of the cutting oradvancing procedure, respectively. In an advantageous manner, the deviceis further developed such that the anchor drilling and setting devicescomprise at least one optionally remotely controllable switch forstarting the drilling cycle, a filling procedure for introducingadhesive cartridges and a setting procedure for screwing in an anchorbolt.

In order to ensure the particularly rapid securement of the roof andkeep the time required for the anchor drilling and setting procedure asshort as possible, the configuration advantageously is devised such thatthe anchor drilling and setting devices comprise at least two relativelymovable separate carriages for the vertical displacement of themanipulator and the drill rod assembly and the anchor, and that at leastone rotation drive is provided for the drill rod assembly and theanchor, said carriages advantageously being equipped with at least twoseparate end switches for the limitation of the strokes of the rotationdrives. Such a structural configuration of the device renders feasiblethe particularly simple and quick automated controlling, wherein theconfiguration, with a view to increasing the operating safety, may bedevised such that separate switches are provided for the drilling cycleand the anchoring cycle. Separate switches in this context suggest notonly separate end switches for the two cycles, but also separateswitches for the start of the respective method step, namely thedrilling cycle or the anchoring cycle.

Based on such a device, it is feasible in a particularly advantageousmanner to devise the configuration such that the control means for theanchor drilling and setting devices comprise timers for the automaticexecution of the respective cycle, wherein the second carriage isswitched to a defined downward movement between the end of the drillingcycle and prior to the pivotal movement of the manipulator into ananchoring position, whereupon, after the start of the anchoring cyclefor the final partial stroke of the movement of the anchor, the secondcarriage after a defined time-controlled waiting step, upon switching onof a rotation drive, is switched to an upward movement and capable ofbeing moved back into the lowered position subsequently. By pivoting themanipulator between the individual cycles for drilling, introducing theadhesive cartridges and anchoring, a collision with the roof can beprevented, wherein a particularly quick and simple automatic control ofthe anchor drilling and setting procedure at a simultaneous cuttingprocedure is feasible in that the lifting movements of the carriages arecontrolled by end switches and timers.

In the following, the invention will be explained in more detail by wayof an exemplary embodiment schematically illustrated in the drawing aswell as an exemplary embodiment for carrying out the control method. Inthe drawing, FIG. 1 is a side view of a cutting machine comprisinganchor drilling and setting devices supported on the machine frame; andFIG. 2 is a top view on the illustration according to FIG. 1.

FIG. 1 depicts a cutting machine 1, which is movable on a crawlermechanism 2 in the longitudinal direction of the track. A cuttingcylinder 3 rotationally mounted on a cantilever arm 4 is provided towork the mine face, the rotation drive being housed within thecantilever arm 4. The cantilever arm 4 is pivotable in the verticaldirection in the sense of double arrow 5 so as to move the excavationtools over the mine face. Prior to the beginning of an excavation stepthe cutting tools must be introduced into the mine face, to which end abreak-in cutting step is carried out, usually by advancing the cuttingcylinder 3 in a manner that more than half of the cylinder willpenetrate into the mince face, before the cutting procedure proper iscommenced by a downward pivotal movement in the sense of double arrow 5.Break-in cutting, as a rule, is performed close to the roof by liftingthe cutter arm 4 into the appropriate position for the break-in cut.

Supporting props 6, via which a roof bar 7 can be pressed at the roof inorder to stabilize the machine within the track, bear against themachine frame. Furthermore, an additional supporting prop 8 is visible,via which the roof bar is articulately supported on the rear end of themachine.

A haulage means, via which the cut material is thrown onto conveyingmeans arranged within the track such as, for instance, conveying beltsor conveying cars, is schematically illustrated at 9 on the rear end ofthe machine.

Near the mine face, anchor drilling and setting devices 10 are arrangedon the machine frame, with an anchor 11 stored in a magazine and theassociated manipulator 12 being apparent from the side view according toFIG. 1. The manipulator 12 is displaceable in the vertical direction bymeans of a first carriage 13. On said first carriage 13, a secondcarriage 14 is displaceable in the vertical direction relative to thefirst carriage 13. The manipulator is designed to be pivotable about asubstantially vertical axis in order to be able to assume therespectively aligned position with the anchor borehole for the varioussteps of drilling and anchoring and introducing adhesive cartridges,respectively, and in order to be able to remove anchors 11 from therespective magazine.

In the illustration according to FIG. 1, a control means for the anchordrilling and setting devices is, furthermore, schematically indicated at15, which monitors and controls the automated and programmed sequence ofthe individual cycles during drilling and anchoring. Finally, therespective control means for the operation of the cutting cylinder 3 isindicated at 16, via which the individual method steps during cuttingare optionally automatically controlled. At 17, the pertinent networkline which connects control means 15 and 16 in a manner that the twomeans will respectively receive full information on the respectiveworking step of the different devices is indicated.

From the top view according to FIG. 2, a loading ramp 18 is finallyapparent, via which the cut material is taken up from the floor, whereinloading arms 19 convey to a haulage means the material taken up via theloading ramp 18.

In principle, any known control means can be used for the control means15 and 16, the method sequence for controlling essentially comprisingthe following steps:

1. The support and, in particular, the roof bar 7 are positioned andpressed at the roof, whereupon the drill bit of a drill rod of theanchor drilling and setting device 10 is pivoted into the appropriateposition. In this first step, also the positioning of the drill bit mayalready be effected by moving the carriages 13 and 14. The release ofthe drilling cycle is effected following the appropriate message by thecontrol means 16 via line 17, according to which break-in cutting hasbeen completed and the cutting operation proper has started by thedownward pivotal movement of the cantilever arm 4 in the sense of doublearrow 5. Upon release, either an appropriate enabling signal may begenerated or the drilling cycle may be started at once.

2. At the beginning of the drilling cycle, the drill bit is, at first,driven into the roof in a time-controlled manner over a predeterminedperiod of time of, for instance, 2 seconds at low speed and a shortadvance.

3. Immediately after this, the regular drilling procedure takes placewith the advance and advance speed being controllable via the hydraulicpressure or flow rate.

4. After the upward movement of the drilling machine on the carriage 14into its upper end position, in which an end switch may, for instance,be actuated, the number of revolution is reduced and the drill rod isretracted again. At that moment, the second carriage 14 is in its upperend position, which may again be controlled by a separate end switch.Then is positioned the nose piece of a hose through which a fluid, e.g.air under pressure, and adhesive cartridges are introduced. After this,the nose piece of the hose is again pivoted back.

In the third phase of the operating movements of the anchor drilling andsetting device, the consecutive method steps can be initiated eitherautomatically immediately thereupon or by actuating a further switch.

5. After having lowered the second carriage 14 by a defined path or overa defined time of, for instance, 4 seconds, in order to avoid anyimpediment of the pivotal movement of the manipulator, an anchor bolt isremoved from a carrousel or magazine.

6. The threaded drive on the carriage 14 is moved in the verticaldirection and the anchor rod is released by the manipulator so as toenable its introduction initially without rotation at an interval ofseconds and then under rotation. The upward movement of the anchor boltis again effected until the actuation of a separate switch. By therotary movement and further upward movement of the anchor bolt, theadhesive cartridges are destroyed and the emerging material isaccordingly blended.

7. After having reached the end position of the first carriage 13, thesecond carriage 14 is moved upwards over a predetermined period of timeof, for instance, 5 seconds, with the rotation drive intended to turn inthe anchor bolt remaining activated until the predetermined time ofblending of the adhesive has been attained.

8. A waiting cycle of, for instance, 20 seconds is switched on for theadhesive resin to harden.

9. The rotation drive for the anchor bolt is again activated over adefined period of time of, for instance, 2 seconds in order to tightenthe anchor bolt.

10. The second carriage 14 is again lowered as far as to the mechanicalend stop. After this, the threaded drive is retracted into its lower endposition, whereby an end switch may again be actuated in this case. Whenusing separate drives for the drilling motor and the tightening of theanchor bolts, the drilling motor is subsequently pivoted in again.

A further working cycle takes place after the cutting machine hasreached a new position, i.e. following a further break-in cuttingprocedure, wherein the distance over which an anchorage iseffected—viewed in the longitudinal direction of the track—depends onthe nature of the material of the roof, anchoring being not necessarilyrequired after each new break-in cutting procedure, but only after amultiple of such break-in cutting procedures.

The termination of the working cycles of the anchor drilling and settingdevice is again appropriately signalized in order to indicate that theroof has now been secured and a new break-in cutting procedure may beeffected. During those phases of the process, all of the devices andmeans are the region secured by anchors such that the respectivemagazines can again be filled with anchor rods and the respectivelycorrect starting position for the automatic sequence of the workingcycles during anchoring and drilling can be resumed.

The operators will be in a dust- and noise-protected cabin duringanchoring off. By using radio remote control for the control of theanchor drilling and setting device and the tunneling or mining machine,any control may also be effected from above ground.

1. A method for drilling and setting adhesive anchor bolts close to amine face during a cutting operation of a tunneling or mining machine(1) capable of being displaced on a traveling mechanism (2) andincluding a cutting cylinder (3) or cutting head rotationally mounted ona cantilever arm (4) pivotable in a vertical direction (5), andoptionally in a horizontal direction, comprising the steps of detectinga substantially horizontal forward movement of the cantilever arm (4)during break-in cutting, and generating a signal during break-in cuttingto block commencement of a working cycle for drilling and anchoring. 2.A method according to claim 1, wherein commencement of an anchordrilling and setting procedure is enabled upon completion of thehorizontal movement of the cantilever arm (4) into the mine face.
 3. Adevice for drilling and setting adhesive anchor bolts close to a mineface during a cutting operation of a tunneling or mining machine (1)capable of being displaced on a traveling mechanism (2) and including acutting cylinder (3) or cutting head rotationally mounted on acantilever arm (4) pivotable in a vertical direction (5), and optionallyin a horizontal direction, comprising means for detecting asubstantially horizontal forward movement of the cantilever arm (4)during break-in cutting; means for generating a signal during break-incutting to black commencement of a working cycle for drilling andanchoring; and means for controlling excavation of material (16) on themine face networked with means for controlling actuation (15) of atleast one anchor drilling and setting device (10) via at least one ofradio, electrical, and optical lines.
 4. A device according to claim 3,wherein the at least one anchor drilling and setting device (10)comprises at least one, optionally remotely controllable, switch forstarting a drilling cycle, a filling procedure for introduction ofadhesive cartridges, and a setting procedure for screwing in an anchorbolt.
 5. A device according to claim 4, wherein the at least one anchordrilling and setting device (10) comprises a plurality of relativelymovable separate carriages (13, 14) for vertical displacement of amanipulator (12) and a drill rod assembly and an anchor (11), and atleast one rotation drive is provided for the drill rod assembly and theanchor (11).
 6. A device according to claim 5, wherein the carriages(13, 14) comprise at least two separate end switches for limitation ofstrokes.
 7. A device according to claim 6, comprising separate switchesfor the drilling cycle and for an anchoring cycle.
 8. A device accordingto claim 7, wherein the means for controlling actuation (15) of theleast one anchor drilling and setting device (10) comprises at least onetimer for automatic execution of drilling cycles and anchoring cycles,wherein a second carriage (14) is switched to a defined downwardmovement between end of the drilling cycle and prior to pivotal movementof the manipulator (12) into an anchoring position, whereupon, aftercommencement of the anchoring cycle for a final partial stroke ofmovement of the anchor (11), the second carriage (14) after a definedtime-controlled waiting step, upon switching on of a rotation drive, isswitched to an upward movement and is capable of being moved back into alowered position subsequently.
 9. A device according to claim 6, whereinthe means for controlling actuation (15) of the at least one anchordrilling and setting device (10) comprises at least one timer forautomatic execution of drilling cycles and anchoring cycles, wherein asecond carriage (14) is switched to a defined downward movement betweenend of the drilling cycle and prior to pivotal movement of themanipulator (12) into an anchoring position, whereupon, aftercommencement of the anchoring cycle for a final partial stroke ofmovement of the anchor (11), the second carriage (14) after a definedtime-controlled waiting step, upon switching on of a rotation drive, isswitched to an upward movement and is capable of being moved back into alowered position subsequently.
 10. A device according to claim 6,wherein lifting movements of the carriages (13, 14) are controlled byend switches and timers.
 11. A device according to claim 5, comprisingseparate switches for the drilling cycle and for an anchoring cycle. 12.A device according to claim 11, wherein the means for controllingactuation (15) of the at least one anchor drilling and setting device(10) comprises at least one timer for automatic execution of drillingcycles and anchoring cycles, wherein a second carriage (14) is switchedto a defined downward movement between end of the drilling cycle andprior to pivotal movement of the manipulator (12) into an anchoringposition, whereupon, after commencement of the anchoring cycle for afinal partial stroke of movement of the anchor (11), the second carriage(14) after a defined time-controlled waiting step, upon switching on ofa rotation.
 13. A device according to claim 11, wherein liftingmovements of the carriage (13, 14) are controlled by end switches andtimers.
 14. A device according to claim 5, wherein the means forcontrolling actuation (15) of the at least one anchor drilling andsetting device (10) comprises at least one timer for automatic executionof drilling cycles and anchoring cycles, wherein a second carriage (14)is switched to a defined downward movement between end of the drillingcycle and prior to pivotal movement of the manipulator (12) into ananchoring position, whereupon, after commencement of the anchoring cyclefor a final partial stroke of movement of the anchor (11), the secondcarriage (14) after a defined time-controlled waiting step, uponswitching on of a rotation drive, is switched to an upward movement andis capable of being moved back into a lowered position subsequently. 15.A device according to claim 5, wherein lifting movements of thecarriages (13, 14) are controlled by end switches and timers.
 16. Adevice according to claim 4, comprising separate switches for thedrilling cycle and for an anchoring cycle.
 17. A device according toclaim 16, wherein the means for controlling actuation (15) of the atleast one anchor drilling and setting device (10) comprises at least onetimer for automatic execution of drilling cycles and anchoring cycles,wherein a second carriage (14) is switched to a defined downwardmovement between end of the drilling cycle and prior to pivotal movementof the manipulator (12) into an anchoring position, whereupon, aftercommencement of the anchoring cycle for a final partial stroke ofmovement of the anchor (11), the second carriage (14) after a definedtime-controlled waiting step, upon switching on of a rotation drive, isswitched to an upward movement and is capable of being moved back into alowered position subsequently.
 18. A device according to claim 16,wherein lifting movements of the carriages (13, 14) are controlled byend switches and timers.
 19. A device according to claim 3, wherein theat least one anchor drilling and setting device (10) comprises aplurality of relatively movable separate carriages (13, 14) for verticaldisplacement of a manipulator (12) and a drill rod assembly and ananchor (11), and at least one rotation drive is provided for the drillrod assembly and the anchor (11).
 20. A device according to claim 19,wherein the carriages (13, 14) comprise at least two separate endswitches for limitation of strokes.
 21. A device according to claim 20,comprising separate switches for the drilling cycle and for an anchoringcycle.
 22. A device according to claim 21, wherein the means forcontrolling actuation (15) of the at least one anchor drilling andsetting device (10) comprises at least one timer for automatic executionof drilling cycles and anchoring cycles, wherein a second carriage (14)is switched to a defined downward movement between end of the drillingcycle and prior to pivot movement of the manipulate (12) into ananchoring position, whereupon, after commencement of the anchoring cyclefor a final partial stroke of movement of the anchor (11), the secondcarriage 14) after a defined time-controlled waiting step, uponswitching on of a rotation drive, is switched to an upward movement andis capable of being moved back into a lowered position subsequently. 23.A device according to claim 21, wherein lifting movements of thecarriages (13, 14) are controlled by end switches and timers.
 24. Adevice according to claim 20, wherein the means for controllingactuation (15) of the at least one anchor drilling and setting device(10) comprises at least one timer for automatic execution of drillingcycles and anchoring cycles, wherein a second carriage (14) is switchedto a defined downward movement between end of the drilling cycle andprior to pivotal movement of the manipulator (12) into an anchoringposition, whereupon, after commencement of the anchoring cycle for afinal partial stroke of movement of the anchor (11), the second carriage(14) after a defined time-controlled waiting step, upon switching on ofa rotation drive, is switched to an upward movement and is capable ofbeing moved back into a lowered position subsequently.
 25. A deviceaccording to claim 20, wherein lifting movements of the carriages (13,14) are controlled by end switches and timers.
 26. A device according toclaim 19, comprising separate switches for the drilling cycle and for ananchoring cycle.
 27. A device according to claim 26, wherein the meansfor controlling actuation (15) of the at least one anchor drilling andsetting device (10) comprises at least one timer for automatic executionof drilling cycles and anchoring cycles, wherein a second carnage (14)is switched to a defined downward movement between end of the drillingcycle and prior to pivotal movement of the manipulator (12) into ananchoring position, whereupon, after commencement of the anchoring cyclefor a final partial stroke of movement of the anchor (11), the secondcarnage (14) after a defined time-controlled waiting step, uponswitching on of a rotation drive, is switched to an upward movement andis capable of being moved back into a lowered position subsequently. 28.A device according to claim 26, wherein lifting movements of thecarriages (13, 14) are controlled by end switches and timers.
 29. Adevice according to claim 19, wherein the means for controllingactuation (15) of the at least one anchor drilling and setting device(10) comprises at least one timer for automatic execution of drillingcycles and anchoring cycles, wherein a second carriage (14) is switchedto a defined downward movement between end of the drilling cycle andprior to pivotal movement of the manipulator (12) into an anchoringposition, whereupon, after commencement of the anchoring cycle for afinal partial stroke of movement of the anchor (11), the second carriage(14) after a defined time-controlled waiting step, upon switching on ofa rotation drive, is switched to an upward movement and is capable ofbeing moved back into a lowered position subsequently.
 30. A deviceaccording to claim 29, wherein lifting movements of the carriages (13,14) are controlled by end switches and timers.
 31. A device according toclaim 19, wherein lifting movements of the carriages (13, 14) arecontrolled by end switches and timers.